A Programmable Logic Controller (PLC) is an industrial computer control system that continuously monitors the state of input devices and performs automated decisions based upon a user-designed program to control the state of output devices. Almost any production line, machine function, or process can be greatly enhanced using this type of control system. However, one main benefit in using a PLC is the ability to change and replicate the operation or process while collecting and communicating vital information. Another advantage of a PLC system is that it is modular. That is, users can mix and match the types of Input and Output devices to best suit a given application.
Programmable Logic Controllers are programmed by systems designers to operate manufacturing processes via user-designed logic programs or user programs. The user programs are stored in memory and generally executed by the PLC in a sequential manner although instruction jumping, looping and interrupt routines, for example, are also common. Associated with the user program are a plurality of memory elements or variables that provide dynamics to PLC operations and programs. Differences in PLCs are typically dependent on the number of Input/Output (I/O) they can process, amount of memory, number and type of instructions, and speed of the PLC central processing unit (CPU).
One application that PLCs are particularly well-suited is for controlling the amounts of materials solids, gases or liquids that are employed in manufacture of a given process. In a many industries, materials such as various types of grain are employed to produce the final products. In other applications, various liquids are added and mixed to produce the desired product at hand. In order to successfully manufacture such products in highly automated manner, various measuring techniques are required to determine the amounts of materials that have been added to or mixed with a given process or recipe. In general, measuring devices such as load cells, flow meters, or other devices are employed to automatically measure the amount of product added to a container for example, where instructions within the PLC are utilized to determine the precise amount that has in fact been added to the batch, recipe, or process. Such applications for determining these amounts are referred to as totalizer applications or totalizing applications.
As can be appreciated, integrated manufacturing operations involve high-complexity manufacturing processes. Such processes are involved in many areas of modern production. Often, complex factory equipment arrangements and programming are required to provide the functionality necessary to measure the required amount of materials. This can include significant expense to install and maintain equipment such as load cells and flow meters to measure such materials. In view of such expense, a single means of measuring material amounts required for a given process is often utilized. Single measuring points forces manufacturing processes to perform material additions to the process—one at a time, in order to measure accurately differing materials and material amounts. By causing materials to be added sequentially, process costs are increased due to the increased time to manufacture. Thus, the reduction in overall time to perform these additions is often limited to minimizing the dead-time between sequential material additions.